Antioxidant compositions

ABSTRACT

A composition comprising a food susceptible to lipid oxidation and an extract formed by the aqueous extraction of black tea leaves in a process which includes extraction at a temperature from 120° to 210° C., the amount of extract being such that the content of tea solids present is from 0.005% to 1.5% by weight based on the weight of food.

This is a continuation application of co-pending application Ser. No.620,754, filed June 4, 1984, now abandoned, which is acontinuation-in-part of application Ser. No. 561,678, filed Dec. 15,1983, which is also abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to antioxidants for food substances, moreparticularly to antioxidants obtained by the extraction of tea leaves attemperatures of at least 120° C. as in certain processes for theproduction of instant tea.

Lipid autoxidation occurring in foods has always been a concern for bothfood processors and consumers and the most common method used to inhibitlipid oxidation is the application of synthetic antioxidants which blockthe oxidative reactions. However, owing to toxicological and nutritionalconsiderations, only a very few synthetic antioxidants are permitted infood applications, e.g., butylhydroxytoluene (BHT), butylhydroxyanisole(BHA), propyl gallate (PG) and t-butyl hydroquinone (TBHQ). Even theseantioxidants are now being examined by regulator agencies and consumeractivists and these developments have urged the need to exploit newsources of natural antioxidants.

One natural product with excellent antioxidant properties, Rosemary AR,suffers from the disadvantage of having a very intensive characteristicherb flavour which may limit its use in some applications.

It is also reported in the literature that certain tea extracts haveantioxidant properties, e.g., extracts of tea leaves, tea grounds, teasweepings and tea wastes, but in all the tea extracts so far described,the antioxidant activity is generally very low and the application ofeach extract is limited to a restricted class of food materials. As faras we are aware no study on the antioxidant properties of instant tea orthe intermediate extracts produced during its manufacture has beendocumented.

SUMMARY OF THE INVENTION

We have found surprisingly, that in the aqueous extractions of black tealeaves at temperatures from 120° C. to 210° C., certain extracts areformed which contain appreciable quantities of gallic acid. Theseextracts have an antioxidant activity comparable with or superior tosynthetic antioxidant systems, and they do not suffer from the intensiveflavour problem of Rosemary AR. In addition, these extracts areeffective in a much wider variety of food systems than tea extractspreviously described as having antioxidant activity. Unlike conventionalantioxidants, they are both oil and water soluble and this property isespecially advantageous when the food systems are oil-in-water emulsionsand water-in-oil emulsions. Still further, we have also found that theseextracts, by soaking uncooked roast beef overnight in a tea extractsolution of about 0.25% by weight, are useful in inhibiting the"warmed-over" flavor commonly associated with cooked roast beef whichhas been reheated.

Accordingly, the present invention provides a composition comprising afood susceptible to lipid oxidation and an extract formed by the aqueousextraction of black tea leaves in a process which includes a treatmentat a temperature from 1210° C. to 210° C., the amount of extract beingsuch that the content of tea solids present is from 0.005% to 1.5% byweight based on the weight of food, said extract containing at least 5%by weight of phenol compounds based on the weight of tea solids.

Food materials that may be stabilized against oxidation are, forexample, frying oils and fats, potato flakes, bakery products, meatemulsions, precooked cereals, instant noodles, soybean milk, chickenproducts, emulsion products such as sausage, mayonnaise and margarine,frozen fish, frozen pizza, cheese and animal foods.

Instant tea is routinely prepared by the hot water extraction of tealeaves, for example, as described in World Coffee and Tea, April 1972,pages 54-57, "The practice of instant tea manufacture". In the presentinvention, similar extraction conditions used in instant tea manufactureare followed wherein at least part of the extraction of the tea leavesis carried out at a temperature of at least 120° C. to obtain the teaextracts with valuable antioxidant properties. Those extracts as well asthe spent tea leaves or residues remaining after extraction, and theinstant tea powder have antioxidant properties. For convenience, theword "extract" used in this invention includes the instant tea powder,the spent tea leaves and residues, including tea grounds, tea sweepingsand tea wastes, after extraction. The concentrated extracts containingup to 15% tea solids, especially from 4% to 105 tea solids haveespecially good antioxidant activity.

DESCRIPTION OF PREFERRED EMBODIMENTS

In one particular process of making tea antioxidant, black tea leavesare extracted at a temperature from 80° C. to 130° C. to give an initialextract (Fraction I). The residual leaves are extracted at a temperaturefrom 120° C. to 210° C. and centrifuged to give a second extract(Fraction II). Fraction I and Fraction Ii are combined and concentratedto give an approximately 5-10% tea concentrate which is cooled and theinsoluble tannins separated therefrom to give a water soluble tea liquor(Fraction III). All fractions are further concentrated and dried.Preferably the tea leaves are extracted at a temperature from 100° C. to125° C. and especially from 105° C. to 120° C., for a period from 10minutes to 60 minutes to give the initial extract. The residual tealeaves are then milled, slurried and extracted again conveniently for aperiod from 5 to 60 minutes, preferably from 20 to 40 minutes, at atemperature from 130° C. to 210° C., preferably from 145° C. to 195° C.,more preferably from 160° C. to 185° C., and especially from 165° C. to180° C. Advantageously, the extraction at the higher temperatures iscarried out under pressure, the preferred pressures used ranging from 1bar at 130° C. to 15 bars at 210° C. After this second extraction thetea residue is removed by centrifugation to yield Fraction II. In thisprocess, Fraction I, Fraction II, Fraction III, the residual tea leavesand the ultimately produced instant tea all have significant antioxidantactivity, and especially Fraction II and Fraction III.

In particular, appreciable antioxidant activity is possessed by thevarious extracts, the residual tea leaves and also the instant teaproduced in the processes described in U.S. Pat. No. 3,451,823.

Excellent antioxidant activity is obtained when the amount of phenolcompounds is at least 5% by weight and preferably at least 8% by weightbased on the weight of tea solids.

The major phenolic constituents of the tea solids and the amount of eachusually present in the extracts are gallic acid (0.05 to 1.5%),epicatechnin (0.01 to 0.5%), catechin (0.01 to 0.6%), epigallocatechin(0.01 to 0.75), epicatechin gallate (0.01 to 1.00%) and epigallocatechingallate (0.01 to 1.5%), all the amounts being given as percentages byweight based on the weight of tea solids. The amount of extract presentin the food is conveniently such that the tea solids content is from0.008 to 1.00% by weight, preferably from 0.02 to 0.75% and especiallyfrom 0.05 to 0.5% by weight based on the weight of food. The teaextracts show antioxidative synergism in food either with ascorbic acidor with lecithin. The amount of ascorbic acid or lecithin used in asynergistic mixture may be from 0.02 to 2.00%, preferably from 0.05 to1.00% by weight based on the weight of food, while the amount of extractis conveniently such that the solids content is from 0.01 to 0.5% byweight based on the weight of food.

In a preferred embodiment of the present invention, the tea extracts maybe further extracted with a water-immiscible organic solvent capable ofextracting at least a part of the phenol compounds from the extracts,for example, by partitioning. Examples of such solvents are petroleumether, pentane, diethyl ether, hexane, ethyl propionate, ethyl acetate,methyl iso-butyl ketone or halogenated hydrocarbons such as Freons. Theextracted polyphenols may then be separated, for example, by removal ofthe solvent by rotary evaporation, and reconstituted with water andfreeze-dried. Such phenolic-containing extracts have superiorantioxidant activity and oil solubility to the tea extracts from whichthey are extracted.

In another embodiment of this invention, the Fraction I extract may beheated at a temperature from 130° C. to 210° C., preferably from 160° C.to 210° C., for a period of, for instance, 10 to 60 minutes to give anextract with improved antioxidative effectiveness.

In yet another embodiment of the present invention, the tea extracts maybe treated with tannase to increase the antioxidant activity. Thetreatment with tannase is preferably carried out at a pH from 4.0 to5.5, especially from 4.5 to 5.0. The amount of the tannase used to treatthe tea extract is not critical but usually an amount from 0.02% to 1.0%by weight based on the weight of tea solids is effective andconveniently an amount from 0.05% to 0.5% by weight based on the weightof tea extract may be used. The synergistic antioxidant effect withascorbic acid is especially marked when the tea extracts are treatedwith tannase, especially at low levels of application, e.g., 0.02% to0.05% by weight of solids based on the weight of food.

EXAMPLES

The following examples further illustrate the present invention.

Example 1

Black tea leaves are extracted at a temperature between 110° C. and 120°C. for 30 minutes to give Fraction I. The residual tea leaves aremilled, slurried and then extracted at 190° C. and a pressure of 11 barsfor a further 30 minutes. This slurry was centrifuged and thesupernatant was recovered as Fraction II. A combination of Fraction Iand Fraction II was then concentrated to give a 5-10% tea concentratewhich was cooled to a temperature of 15° C. to precipitate the insolubletannins. The tea liquor was then centrifuged and the insoluble tanninsremoved to give Fraction III.

Samples of Fraction II and Fraction III, respectively, were incorporatedinto separate 100g batches of chicken fat in amounts such that thecontent of tea solids in each batch was 0.05% by weight based on theweight of the chicken fat. In addition, a mixture of Fraction II andascorbic acid (AA) was incorporated into a further 100g batch of chickenfat wherein the amount of Fraction II was such that the content of teasolids in the batch was 0.10% by weight based on the weight of chickenfat and the amount of ascorbic acid was 0.05% by weight based on theweight of chicken fat. As a comparison 0.01g of BHA was incorporated ina further 100g batch of chicken fat. The antioxidative activity wasdetermined by a modified Rancimat Method which is an acceleratedoxidation test described by J. Frank, J. Geil and R. Freaso in "FoodTechnology 1982, Vol. 36, No. 6, p. 71", in chicken fat at 100° C. Theoxidative stability of the chicken fat was determined by the inductionperiod (IP), the time required for the fat to become rancid. Tofacilitate comparison of the data, the antioxidant index (AI), definedas the induction period of the treatment divided by the induction periodof the control was used to report the effectiveness of the antioxidants.In the test, frozen chicken fat was melted directly over low heat on astove top. The test antioxidants were incorporated directly into 100gsamples of the melted fat and homogenised. Ten gram samples of thecontrol chicken fat, and chicken fat containing the antioxidant werethen placed in the Rancimat reaction vessels for the acceleratedoxidation test. The test temperature was 110° C. instead of 100° C.which is prescribed by the Rancimat Method noted above. This was theonly modification made to the Rancimat procedure. The air flow rate was20 liter hr. The results are as shown in Table I:

                  TABLE I                                                         ______________________________________                                               ANTIOXIDANT AI                                                         ______________________________________                                               Fraction II 3.6                                                               Fraction III                                                                              5.0                                                               Fraction II and AA                                                                        6.4                                                               BHA         6.0                                                        ______________________________________                                    

These results showed that the antioxidant activity of the tea extractswere comparable with that of a commercial synthetic antioxidant.

Example 2

Samples of Fraction I, Fraction II, residual tea leaves and Fraction IIIformed in the process described in Example 1 were incorporated intochicken fat at various concentrations and tested in exactly the same wayas described in Example 1. The values of the antioxidant activity (AI)at the various concentrations given as the % content of tea solidspresent in the chicken fat are shown in Table II:

                  TABLE II                                                        ______________________________________                                                   Tea Solids (% Concentration)                                       Antioxidant  0.05   0.10       0.50  1.0                                      ______________________________________                                        Fraction I   1.5    1.8         3.4  --                                       Fraction II  3.6    6.2        13.2  15.6                                     Residual Tea Leaves                                                                        1.0    1.6         3.0   2.8                                     Fraction III 5.0    8.0        18.0  21.7                                     Instant Tea Powder                                                                         1.8    2.2         4.6   7.3                                     ______________________________________                                    

No flavour from the tea extracts was imparted to the chicken fat even at1% concentration.

Example 3

Individual samples of Fraction II formed in the process described inExample 1, soy lecithin and mixtures thereof were incorporated intochicken fat at the concentrations indicated in Table III and tested inexactly the same way as described in Example I. The induction period ofthe chicken fat without additives, the induction period of the chickenfat containing the specified additives, as well as the % synergism ofthe mixtures of Fraction II and soy lecithin are indicated in Table III.

                  TABLE III                                                       ______________________________________                                        Sample         Induction period (hr)                                                                        % synergism                                     ______________________________________                                        Control        1.0            --                                              Fraction II, 500 ppm                                                                         3.0            --                                              Lecithin*, 500 ppm                                                                           1.2            --                                              Fraction II, 500 ppm and                                                                     4.3            33.3                                            lecithin, 500 ppm                                                             Lecithin, 1000 ppm                                                                           1.4            --                                              Fraction II, 500 ppm and                                                                     4.9            38.5                                            lecithin, 1000 ppm                                                            ______________________________________                                         *Centrolex f lecithin, Central Soya                                           ##STR1##                                                                      IL = Induction period of substrate                                            IA = Induction period of primary antioxidant                                  IS = Induction period of synergist                                            IM = Induction period of primary antioxidant/synergist                   

Example 4

Samples of Fraction I and Fraction II formed in the process described inExample 1 were each made into 3% aqueous solutions. To each solutionwere added two volumes of ethyl acetate to form two immiscible layers.The organic layer was collected and the procedure of extraction wasrepeated twice. The pooled organic layer was rotary evaporated and theresidue freeze dried. The yield was 31% for Fraction I and 9% forFraction II.

Samples of Fraction I, Fraction II, the organic solvent of Fraction I(Fraction IA) and the organic extract of Fraction II (Fraction IIA) wereincorporated into chicken fat at a solids content of 500 ppm and theantioxidant index (AI) was determined as described in Example 1. Theresults are given in Table IV and illustrate the improved antioxidantactivity of the organic extract compared with the aqueous extract.

                  TABLE IV                                                        ______________________________________                                        Instant Tea Extract                                                                             AI                                                          ______________________________________                                        Fraction I        2.1                                                         Fraction II       3.8                                                         Fraction IA       7.8                                                         Fraction IIA      11.6                                                        ______________________________________                                    

Example 5

A sample of Fraction I formed in the process described in Example I washeated at 190° C. for 30 minutes. Samples of Fraction I and the treatedFraction I were incorporated into chicken fat at a solids content of 500ppm and the antioxidant index measured in the way described in Example 1was found to be 2.4 for Fraction I and 4.1 for treated Fraction I, animprovement of 70%.

Example 6

A sample of Fraction I formed in the process described in Example 1 wasmixed for 1 hour at 45° C. and at pH 4.5 with 0.1% by weight based onthe weight of Fraction I of tannase obtained from Enzyme DevelopmentCompany, NY, NY. Samples of Fraction I and the tannase treated FractionI were incorporated into chicken fat at a solids content of 500 ppm andthe antioxidant index measured in the way described in Example 1 wasfound to be 1.5 for Fraction I and 2.8 for the tannase treated FractionI showing that the tannase treatment almost doubled the antioxidantactivity of Fraction I.

Example 7

Samples of Fraction I formed in the process described in Example 1,Fraction I treated with tannase as described in Example 6, and a mixtureof 85 parts of a tannase treated Fraction I and 15 parts of ascorbicacid were incorporated into separate samples of chicken fat at a solidscontent concentration indicated in Table V. The antioxidant index (AI)of each sample was measured in the way described in Example 1 and thevalues of the AI at the various concentrations are shown in Table V.

                  TABLE V                                                         ______________________________________                                                Tea solids (% concentration in chicken fat)                           Antioxidant                                                                             0.025    0.05    0.10   0.25  0.50                                  ______________________________________                                        Fraction I                                                                              1.2      1.4     1.8    2.7   3.4                                   Tannase treated                                                                         1.6      2.5     3.4    4.6   4.7                                   Fraction I                                                                    Tannase treated                                                                         3.5      4.5     4.8    5.8   7.1                                   Fraction I +                                                                  Ascorbic acid                                                                 ______________________________________                                    

These results show that there is excellent synergism between tannasetreated Fraction I and ascorbic acid, especially at solidsconcentrations of 0.025% and 0.05%.

Example 8

The effectiveness of Fraction II and solvent extracted Fraction II asprepared in Example 4 of the present invention was tested in pork bymixing each extract at a solids concentration shown in Table VI with1000g portions of fresh ground pork in a Hobart Mixer (Model Nr. K5-A)on a setting of 2 for 3 minutes. Fraction II was added to 20ml waterbefore being mixed with the pork whereas solvent extracted Fraction IIwas mixed with 2.5ml ethanol and then incorporated into 20ml water toaid dispersion. The tea antioxidants of the present invention werecompared with the fat soluble antioxidants Rosemary AR and a mixture ofBHA and BHT which were also mixed with 2.5ml ethanol and thenincorporated into 20ml water before adding to the pork. 25g portions ofeach batch of pork containing the antioxidants as well as a 25g portionof fresh ground pork not containing any added antioxidants were packedin air-permeable plastic films and stored for one week at 4° C. Theantioxidant effectiveness was evaluated by a sensor evaluation panel andthe results are shown in Table VI.

                  TABLE VI                                                        ______________________________________                                        TREATMENT          Rank    Comments                                           ______________________________________                                        Control (no additives)                                                                           5       Spoiled, rancid                                    Fraction II (1000 ppm)                                                                           2       Fresh meat aroma                                   Solvent extract (500 ppm)                                                                        1       Fresh meat aroma                                   Rosemary AR (500 ppm)                                                                            4       Rosemary odour                                     BHA (100 ppm) & BHT (100 ppm)                                                                    3       Slight off-odour                                   ______________________________________                                    

Example 9

The effectiveness of a solvent extracted Fraction II as prepared inExample 4 of the present invention was tested in both pork and beef at asolids concentration of 250 ppm in 100g portions of fresh ground porkand beef. The solvent extracted Fraction II was mixed with 2.5ml ethanoland then incorporated into 20ml water before being mixed with the meatin a Hobart Mixer (Model Nr. K5-A) on a setting of 2 for 3 minutes. 25gportions of each batch of pork and beef containing solvent extract aswell as 25g control portions of pork and beef not containing any addedantioxidants were packed in air-permeable plastic films and stored for 8days at 4° C. The antioxidant effectiveness was evaluated by thechemical TBA (thiobarbituric acid) method following as generalguideline, the procedure of Tarladgis et al. 1960. J. Am. Oil Chem. Soc.37:44. The results given in Table VII show clearly the superiorantioxidant activity of the solvent extracts of the present invention.

                  TABLE VII                                                       ______________________________________                                        SAMPLE            TBA Value*                                                  ______________________________________                                        Pork Control      0.44                                                        Pork + Solvent Extract                                                                          0.22                                                        Beef Control      1.27                                                        Beef + Solvent Extract                                                                          0.38                                                        ______________________________________                                         *mg malonaldehyde per 1000 g sample.                                     

We claim:
 1. A composition comprising a food susceptible to lipidoxidation and a black tea extract containing 0.005% to 1.5% tea solidsbased upon the weight of the food, wherein the extract has been obtainedby aqueous extraction of black tea at a temperature of from 130° C. to210° C. and is selected from the group consisting of aqueous extracts,spent tea leaves, residues from the extraction of the black tea, andinstant tea powder and combinations thereof.
 2. A composition accordingto claim 1 wherein the black tea is extracted for a period of from 10minutes to 60 minutes.
 3. A composition as claimed in claim 1 whereinthe tea solids contain phenol compounds in an amount of at least 5% byweight based upon the weight of the tea solids.
 4. A compositionaccording to claim 1 or 3 wherein the extract has been treated withtannase.
 5. A composition according to claim 4 further comprising amaterial selected from the group consisting of ascorbic acid andlecithin and combinations thereof.
 6. A composition according to claim 1or 3 further comprising a material selected from the group consisting ofascorbic acid and lecithin and combinations thereof.
 7. A compositionaccording to claim 1 or 3 wherein precipitated tannins are removed fromthe extract.
 8. A composition according to claim 1 or 3 wherein saidfood susceptible to lipid oxidation is a food selected from the groupconsisting of frying oils, frying fats, potato flakes, bakery products,meat emulsions, precooked cereals, instant noodles, soybean milk,chicken products, sausage, mayonnaise, margarine, frozen fish, frozenpizza, cheese, pork and beef.
 9. A composition according to claim 1wherein the extract has been obtained at a temperature of from 145° C.to 195° C.
 10. A composition according to claim 1 wherein the extracthas been obtained at a temperature of from 160° C. to 185° C.